Minimum reading pressure gage with dual function sensor

Abstract

An electronic device for observing temperature and pressure and for indicating pressure, especially very low pressures. The device has a single sensor element for responding to both temperature and pressure. The device includes a sequence timer for causing the device to first observe the resistance of the sensor when the device is first turned on. The timer then applies a voltage across the sensor, causing a known current to flow through the sensor. The current heats the sensor an amount corresponding to density and therefore the pressure of the gas to which it is exposed. A calculating device is provided for calculating the temperature from the observed value of the initial sensor resistance and the pressure from the observed values of current flow and subsequent sensor resistance. A display is provided for indicating the calculated pressure.

We claim: 
     
       1. Electric apparatus for displaying gas pressure measured at a point, the gas having an ambient temperature and a density, the apparatus comprising, a first data memory (16) for storing ambient temperature related values,   a second data memory (44) for storing minimum pressure related values,   single transducer means (20) positioned at the point for responding both to ambient temperature and to gas density, the transducer (20) having an electrical resistance functionally related to its temperature,   switch means (34) for starting a cycle,   means (12,14) for timing and for establishing a sequence of pressure measurement operations within the cycle,   means (12,18,22,24,42) for measuring the resistance of the transducer means at the start of the cycle,   means (12,14)(68,72) for employing the measured resistance of the transducer means and the functional relationship between the transducer resistance and temperature to calculate ambient temperature related values of the transducer means and to store the calculated temperature related values in the first data memory (16),   means (42,18) for passing a current through the transducer means for heating it whereby the transducer assumes a temperature related to the gas density at the point, and   means (12,22,24) (80,84) for measuring the resistance of the heated transducer means and calculating therefrom (12,16,44) a value related to the pressure at the point from the ambient temperature related value stored in the first data memory (16) and the density related resistance of the heated transducer, further including display means (26) and   means (28) for transmitting the calculated pressure related value to the display means whereby the pressure related value is displayed.     
     
     
       2. Gas pressure measuring and displaying apparatus as recited in claim 1, further providing that among the sequence of operations provided within the cycle are means (14,12) (116,125) for stopping current flow to the transducer means for a time period and means (62,125) for subsequently beginning a new cycle.   
     
     
       3. Gas pressure measuring and displaying apparatus as recited in claim 1, further including means (FIG. 2) for reading, calculating and storing a first set of calculated pressure related values, and   means (FIG. 2) for reading and calculating a second set of pressure related values, and   means (FIG. 3) for securing the difference between the first and the second pressures corresponding to the first and second pressure related values and   means (14,12,28,36) for displaying the pressure difference.   
     
     
       4. Gas pressure measuring and displaying apparatus as recited in claim 3, further providing, means (12) for measuring the time interval between a first and a second reading,   means (12) (91) for dividing the pressure difference between the first and second readings by the time interval, whereby a time rate of pressure change is obtained and   means (28,36) (90) for displaying the time rate of change.   
     
     
       5. Gas pressure measuring and displaying apparatus as recited in claim 3, further providing a device (39) requiring activation;   means (12,14) for defining and storing a difference value,   means (12) (87) for comparing each successive difference value with the defined value, and   means (87,89) for activating the device when any difference value has an established relationship with the defined value.   
     
     
       6. Gas pressure measuring and displaying apparatus as recited in claim 1, further including means (100,104) for storing initial pressure related values in the minimum pressure data memory (44) and   means (88) for comparing the pressure corresponding to each set of newly calculated pressure related values with the pressure corresponding to the pressure related values stored in the minimum pressure data memory (44), and further providing   means (12,14,44) (88,92) for storing in the minimum pressure data memory (44) the newly observed pressure related values, on the condition that the newly observed pressure related values represent a lower pressure than the pressure represented by the pressure related values already stored in the minimum pressure data memory (FIGS. 1,2), and further providing   means (96,100,108) for transmitting the pressure related value stored in the minimum pressure data memory (44), to the display means for temporary display thereon.   
     
     
       7. Gas pressure measuring and displaying apparatus as recited in claim 6, further providing, second display means (36) and means (12,14) for causing the contents of the minimum pressure data storage (44) to be displayed continuously as a pressure in the second display means (36), whereby both the newly observed pressure and the stored lowest observed pressure are simultaneously visible.   
     
     
       8. Gas pressure measuring and displaying apparatus as recited in claim 6, including means (14,12) (116,124,128) for ending the cycle, and further providing that the minimum pressure data memory (44) includes means for retaining its pressure related values after the end of the cycle.   
     
     
       9. Gas pressure measuring and displaying apparatus as recited in claim 6, where the means (34) for causing the temporary display of the minimum pressure are the switch means. 
     
     
       10. Gas pressure measuring and displaying apparatus as recited in claim 9, where the switch means (34) for causing the temporary minimum pressure display is the same switch means used for starting the cycle. 
     
     
       11. Gas pressure measuring and displaying apparatus as recited in claim 9, further providing that among the sequence of operations provided within the cycle are means (14,12) (116,124) for ending the cycle.   
     
     
       12. Means for displaying gas pressure measured at a point and generating pressure related values, the gas having a temperature and a density, the means comprising: display means (26),   a data memory (44) for storing pressure related values including values related to minimum pressure,   transducer means (20) positioned at the point for responding to gas density, the transducer means having an electrical resistance functionally related to its temperature,   clock means (12) for establishing a repeating cycle,   means (12,18,42) for heating the transducer means,   means within the cycle for measuring (12,18,22,24,42) a first and a second resistance of the heated transducer means and for calculating (12) a first and a second value related to the pressure at the point employing in the calculation the resistance of the heated transducer means,   means (28,26) for converting the first pressure related value to an observable pressure value and for storing it in the data memory and for displaying it,   means (44) for converting the second pressure related value to an observable pressure value and for comparing the second pressure value with the stored value, and   means for replacing the stored value with the second pressure value on the condition that the second pressure value represents a lower pressure than the pressure represented by the stored value and further providing   means (34,28,26) (96,100,108,112) for causing the pressure related values stored in the minimum pressure data memory (44) to be temporarily displayed in the display means as a pressure.   
     
     
       13. Gas pressure measuring and displaying means as recited in claim 12 where the means (34) for causing the temporary display of the minimum pressure are switch means. 
     
     
       14. Gas pressure measuring and displaying means as recited in claim 12, further providing second display means (36) and   means (12,14) for causing the contents of the minimum pressure data storage to be displayed continuously as a pressure in the second display means whereby both the currently observed pressure and the past lowest observed pressure are simultaneously visible.   
     
     
       15. Gas pressure measuring and displaying means as recited in claim 12, further providing that the data memory (44) for storing the minimum pressure related value is non-volatile. 
     
     
       16. Gas pressure measuring and displaying means as recited in claim 12, further including means for reading, calculating and storing a first calculated pressure related value,   means for reading and calculating a second pressure related value,   means (85) for securing the difference between the first and the second pressures corresponding to the first and second pressure related values and displaying said difference.   
     
     
       17. Gas pressure measuring and displaying means as recited in claim 16, further providing a device requiring activation (39),   means (14) for defining and storing a pressure difference value,   means (12,87) for comparing each successive pressure difference value with the defined value, and   means (12,87) for activating the device when any pressure difference value has an established relationship with the defined value.   
     
     
       18. Gas pressure measuring and displaying means as recited in claim 16, further providing means (14,12) for measuring the time interval between each first and second reading,   means (14,12) (91) for dividing the pressure difference between the first and second readings by the time interval, whereby a time rate of pressure change is obtained and   means (28,36) (90) for displaying the time rate of change.